In recent years, a sealing pump-up device that, when a pneumatic tire (hereinafter, simply referred to as “tire”) is punctured, without changing a tire and a wheel, injects a liquid sealing agent inside thereof, raises inside pressure of the tire up to designated pressure to repair the tire is prevailing. Among the sealing agents that are used in this kind of sealing pump-up device, there are ones that are produced by stirring and mixing a rubber latex, a resin emulsion and an anti-freeze agent made of propylene glycol. In such a process of production of a sealing agent, in general, in the beginning, the rubber latex and a tackiness agent are mixed to prepare a mixed solution, and an anti-freeze agent is injected into a vessel of the mixed solution to produce a sealing agent stock solution. However, since propylene glycol that is used as an anti-freeze agent is a viscous liquid very strong in the compatibility with water, when propylene glycol is injected in the mixed solution, moisture is rapidly absorbed from the neighboring rubber latex in contact with the propylene glycol. Accordingly, a phenomenon in that a concentration of rubber particles in the surrounding latex becomes very high, rubber particles fuse each other to form aggregates, and the sealing agent is partially or entirely solidified (gelled) with the aggregates as a core tends to occur.
As a process for production of a sealing agent, which intends to inhibit the sealing agent from generating the aggregates, a process described in, for example, Japanese Patent Application Laid-Open (JP-A) No. 2003-342551 is known. A process for production of a sealing agent, which is described in JP-A No. 2003-342551, includes an anti-freeze agent injecting and stirring step where an anti-freeze agent is injected and stirred in a mixed solution of a rubber latex and a stickiness agent contained in a cylindrical vessel. In the anti-freeze agent injecting and stirring step, with the mixed solution stirring by a rotation of a stirring blade of which tip end rotates at such a relatively high speed as 1.0 to 10.0 m/sec, the anti-freeze agent is injected from a plurality of injection ports to a surface of the mixed solution at such a relatively slow speed as 0.01 to 1.0 l/min per one injection port.
According to the process for production of the sealing agent, which is described in JP-A No. 2003-342551, with the mixed solution of rubber latex and a tackiness agent stirring at the speed described above, propylene glycol is injected at a slow injection speed little by little on a surface of the mixed solution. Accordingly, the propylene glycol is inhibited from rapidly absorbing moisture from the periphery thereof to locally raise a concentration of the latex particles. As the result, an advantage in that a plurality of latex particles in the sealing agent stock solution is effectively inhibited from aggregating to form latex aggregates is obtained.
JP-A No. 2003-342551 further describes that, after the injection of the anti-freeze agent (ethylene glycol) has come to completion in the anti-freeze agent injecting and stirring step, the stirring is preferably continued over for some (for example, 5 min or more) time. This is because, when the sealing agent stock solution is continued stirring for a definite time after the injection of ethylene glycol has come to completion, fine latex aggregates generated in the sealing agent stock solution during stirring may be forwarded to aggregate and grow; as the result, the latex aggregates may be more readily removed from the sealing agent stock solution by filtering than when the latex aggregates are present remained fine in the sealing agent stock solution.
Herein, according to knowledge of the present inventors, there is a fear in that when the latex aggregates are insufficiently removed from the sealing agent stock solution and the latex aggregates remain at a predetermined amount or more in a sealing agent as a product, a phenomenon where the sealing agent is forwarded to gel with the latex aggregates as a core is generated, the sealing ability due to the sealing agent to a puncture hole is deteriorated with time, and in a longer time span, the entire sealing agent is gelled to be incapable of injecting in a tire.